Source : Webster's Revised Unabridged Dictionary (1913)

Dispensableness \Dis*pen"sa*ble*ness\, n.
   Quality of being dispensable.

Source : WordNet®

dispensableness
     n : the quality possessed by something that you can get along
         without [syn: {dispensability}] [ant: {indispensability},
          {indispensability}]